I've been working on finding a water source for several weeks. Two days ago I drained the pool to see if some holes dug in some backfilled ditches would finally drain down. They did not drain. The sprinkler system runs 10 minutes a day. The next door neighbor is watering his place at least 20 minutes a day that I know of. The water meter is showing no leaks in the house or sprinkler system. Tested the sprinkler pipes and the pop up heads. So far the only leak is a dribble on one sprinkler head and a possible small leak at the skimmer throat. The tile is still damp around the area where it meets the plastic skimmer after two days of the pool being empty. I suspect that is very small or just water behind the tile because the pool is not loosing water on a bucket test. This pool and home are about 18 months old in a desert mountain area. The lot is held there by a 12' to 20' retaining wall next to the pool. I was worried that I might float the pool when I drained it but all is well after removing all the water and making sure no water leaked back into the pool from the surrounding area. So far it looks like the lot got compacted with some very water proof back fill. I've never heard of anything like this and would like to hear comments from the group. You can check out a youtube video of the job here......

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Hap

http://www.youtube.com/watch?v=zuMXbVJcu9w&mode=user&search=

Hap
Sounds like back fill is super tight and not letting water escape natrually. Sprinklers may have water logged yard after 18 months of coming on. Try boring a few drain off holes in retaining walls to let water out and if it works render some pipes into walls for future draning.
We had the same problem here in London which is built on clay, the sprinklers water logged the garden as water does not go throu' clay quick enough. Had to install land drains just under top soil to keep garden (yard) from drowning.
Good luck.